Insights on the Pulsed-DC Powder-Pack Boriding Process: Effect of current density and electric field implications on the FeB and Fe2B growth kinetics

Abstract

This study examines the impact of current density on the growth kinetics of boride layers during the Pulsed-DC Powder-Pack Boriding (PDCPB). It explores the combined effects of thermally activated diffusion (TD) and electromigration (EM) on boride layer growth kinetics. The analysis assesses how variations in electrical parameters and the properties of the boriding media (particularly electrical resistance and thermal phenomena influenced by components such as KBF₄, B₄C, and SiC) affect overall mass transfer mechanism.

Initial observations indicated a temperature increase related to the Joule effect (~100 K for the entire experimental set), which correlated with the applied current density and the resistive behavior of the semiconductor elements within the boriding media. Additionally, the B activation energies in FeB and Fe₂B phases, estimated at a current density of 460 mA·cm⁻², was found to be ~9 % lower compared to that at 230 mA·cm⁻². A reduction of ~19 % and ~ 25 % in B activation energies for boride layer formation at 230 mA·cm⁻² and 460 mA·cm⁻², respectively, was noted compared to conventional boriding processes.

These findings suggest an enhancement in B diffusivity attributable to the electric field. However, while higher temperatures and current densities shorten the boride layer incubation time, differentiating the contributions of TD and EM remains a challenge.